Folding knife



FIG. 1 is a first side elevational view of a folding knife showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a second side elevational view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevational view thereof; and,

FIG. 6 is a rear elevational view thereof. 

The ornamental design for a folding knife, as shown and described herein. 